Nivation

Nivation is a collective term for a suite of erosional processes that occur beneath and around snow patches or small glaciers. It is primarily a cold-weather process active in periglacial and glacial environments, contributing to the formation and enlargement of hollows or depressions on slopes. While the precise mechanisms and relative importance of each process encompassed by "nivation" are debated, the concept generally includes the following elements:

• Freeze-Thaw Weathering: Repeated cycles of freezing and thawing of water within rock fractures and soil pores weaken the material, leading to its disintegration. The presence of a snow patch promotes this by prolonging the period of time in which temperatures fluctuate around freezing.

• Chemical Weathering: Water derived from melting snow can be slightly acidic, facilitating chemical weathering processes like dissolution of certain minerals. The prolonged presence of water under the snow patch allows more time for these reactions to occur.

• Erosion by Meltwater: Meltwater flowing from the snow patch can erode and transport loose material downslope. The volume and erosive power of meltwater depend on the size and duration of the snowmelt.

• Mass Wasting: The saturated and weakened soil beneath the snow patch is more susceptible to mass wasting processes such as solifluction (slow downslope flow of saturated soil) and soil creep.

The combined effect of these processes results in the gradual excavation of a shallow depression called a nivation hollow or nivation cirque. Over time, these hollows can enlarge and evolve into larger landforms, potentially contributing to the development of cirques in glaciated landscapes. The exact contribution of nivation to cirque formation relative to glacial erosion is still a topic of research.

It is important to note that the term "nivation" is sometimes used loosely and the relative importance of each contributing process can vary depending on local conditions such as rock type, slope angle, and climate.